1. Field of the Invention
The present invention relates to a life estimation device and a life estimation method for a rolling bearing assembly, which are capable of accurately estimating the lifetime and the remaining lifetime of the rolling bearing assembly.
2. Description of Related Art
It has long been known that the lifetime of the rolling bearing assembly depends on various conditions such as including, for example, a working load, a lubricating condition, and materials used to form the rolling bearing assembly. The assessment of the lifetime of the bearing assembly has hitherto been carried out by the utilization of a mathematic calculation life formula that is formulated with due consideration paid to such conditions as, for example, the working load, information condition, and the materials used (See the non-patent document 1 listed below). This mathematic life calculation formula is currently used to estimate the period during which the rolling bearing assembly can be used in service when used under a certain condition, or to estimate the condition under which the rolling bearing assembly can be used without being accompanied by fracture during the required period of service. The rolling bearing assembly is generally used in service under the service condition that is stipulated according to the life formula and, accordingly, no problem ought to occur so long as the bearing assembly is used in service under the ordinary service condition.
It has however been found that the lifetime of the rolling bearing assembly is often of a controversial matter in the market. This appears to be because the rolling bearing assembly actually used is used in service under a condition different from the design condition and/or foreign matters admixed in a lubricating agent brings about an impairment such as, for example, an indentation or the like to a bearing surface layer. For these reasons, some methods have been suggested to estimate the remaining lifetime of the rolling bearing assembly in service. Those remaining lifetime estimation methods hitherto suggested in the art include, inter alia, an off-line method of a kind, in which a change in material of one of rolling bearing assemblies in service that has been sampled out is examined to assess the timing of replacement of the whole bearing assemblies such as discussed in the non-patent document 2 listed below, and an on-line method of a kind in which the conditions of use of the individual bearing assemblies are examined at the site of use thereof to assess the timing of replacement of the individual bearing assemblies such as discussed in any one of the patent documents 1 to 3 listed below.
As one of on-like remaining lifetime estimation methods, a method has been suggested in which the load on the bearing assembly in service, the number of rotations thereof, the condition of a lubricant oil and the size of an indentation formed by the foreign matter are estimated from values given out by various sensors so that the remaining lifetime of such bearing assembly may be estimated such as disclosed in the patent document 3 listed below. According to this method, the relationship between the indentation size and the lifetime of the rolling bearing assembly is expressed by the following formula.L10=L10c×10(0.0038d log(P/C)−0.272 log(d)+0.416)  (1)in which L10 represents 10% lifetime (h), L10c represents the calculated lifetime (h), d represents the diameter of the indentation (μm), P represents the load (kgf), and C represents the dynamic load rating (kgf).